Level 3 PSA - EDF Hinkley Point

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HPC-NNBOSL-U0-000-RES-000028 Version 1.0 Level 3 PSA NOT PROTECTIVELY MARKED Accident group Risk (y -1 ) % of total risk Level 1 PSA (non-core damage)* 1.5E-07 40.4 PCC (not in Level 1 PSA)* 1.0E-07 28.6 EXRV2 2.2E-08 6.1 ADRV 0.0E+00 0.0 Level 2 PSA (core damage) 4.5E-08 12.4 LOSAs 4.6E-08 12.6 Total 3.6E-07 100.0 Table 3 – Risk Contribution by Accident Group The additional accidents identified from the Expert Review of the GDA PSA (EXRV group) can also be seen not to make a significant contribution to the risk, indicating that the accident sequences identified for the PSA and PCC analysis were reasonably comprehensive in relation to risk to workers as well as off-site risk. 5.6.2 Risk Assessment for Other Worker Cohort Groups As previously discussed two other worker cohorts have been defined in addition to the generic worker. These are the Fuel Building and Main Control Room (MCR) worker cohorts. Considering the hierarchy of dominant accidents and their relative Occupancy Factor for a generic worker these two other cohorts are the most relevant to check that the most at risk individual on site has been assessed. The overall risk for these groups has been assessed separately and can be compared against the assessed risk for the generic worker cohort. 5.6.2.1 Main Control Room (MCR) Worker Cohort This worker cohort represents workers in the MCR. This worker cohort is assumed to spend all of their time whilst on-site in the MCR and not to spend any time in other plant areas [AS-013]. As this group of workers is assumed to have to remain in the MCR in the event of an accident, they are assumed to have a maximum likelihood of being exposed to the on-site consequences of accidents anywhere on site, including severe accidents. Therefore, the risk to this group of workers is comprised of the risk from the Level 2 PSA core damage accidents and the off-site consequences [AS-008] of the Level 1 PSA, PCC and expert review accidents. In all cases the occupancy factor for exposure of MCR workers to these accidents is assumed to be unity. For MCR workers only the overall risk figure for comparison against SDO-4 is presented in Section 5.6.3 and Section 5.6.4, both with and without the contribution from LOSAs. 5.6.2.2 Fuel Building Worker Cohort This worker cohort represents a specific group of workers who work exclusively in the fuel building whilst on-site and who do not spend any of their time in any other areas [AS-012]. As such, this group will have the maximum likelihood of exposure to accidents involving fuel handling and accidents involving the spent fuel pool. This cohort will therefore have an occupancy factor of unity for all fuel building accidents and an occupancy factor of zero for all other accidents. A list of the accidents for which the Fuel Building worker cohort is assumed to be affected is given in Table 4 below. 2 Including both local and on-site risk UNCONTROLLED WHEN PRINTED NOT PROTECTIVELY MARKED Page 26 of 60
HPC-NNBOSL-U0-000-RES-000028 Version 1.0 Level 3 PSA NOT PROTECTIVELY MARKED Accident PCC3-02 PCC4-03a PCC4-03b Description Draining of the spent fuel pool Fuel assembly handling accident with damage to 1 row of fuel rods Fuel assembly handling accident with damage to all fuel rods EXRV-05 Heavy object dropped into the spent fuel pool Table 4 – Accidents Considered for the Fuel Building Worker Cohort Unlike the other worker cohorts, this group is assumed not to be affected by the on-site consequences of accidents in other areas, except for the Level 2 PSA core damage accidents for which a worker anywhere on site is assumed to be affected due to the severity of these accidents. For Fuel Building workers only the overall risk figure for comparison against SDO-4 is presented in Section 5.6.3 and 5.6.4, both with and without the contribution from LOSAs. 5.6.3 Worker Cohorts - Risk Excluding LOSAs In addition to the worker cohorts, the risk arising from LOSAs has also been assessed which can be added to the existing risk for any of the worker cohorts, depending upon which cohort would be expected to be required to perform the LOSAs. The overall risk results for the worker cohorts are shown in Table 5 below. Risk (y -1 ) % of SDO-4 BSO Generic worker 3.2E-07 32 MCR worker 6.3E-08 6 Fuel Building worker 2.8E-07 28 Table 5 – Risk Results for Worker Cohort Groups – Excluding LOSAs These results indicate that taking the risk from the generic worker group gives an estimate of risk to an individual worker which is at around 30 % of the SDO-4 BSO. For the MCR workers the risk is assessed to be considerably lower – a factor of 5 less than for the generic worker at 6 % of the SDO-4 BSO. This lower risk is due to the fact that although MCR workers will have a high occupancy factor due to the requirement for them to remain on site during an accident, the dose that they receive from most accidents will be very low compared to workers local to the accident. The Fuel Building worker cohort is assessed as having a risk which is close to the generic worker, at around 30 % of the SDO-4 BSO. 5.6.4 Worker Cohorts - Risk Including LOSAs The overall annual risk results for the worker cohorts, including the risk from LOSAs, are shown in Table 6 below: Risk (y -1 ) % of SDO-4 BSO Generic worker 3.6E-07 36 MCR worker 1.1E-07 11 Fuel Building worker 3.3E-07 33 LOSA performance 4.6E-08 5 Table 6 – Risk Results for Worker Cohort Groups – Including LOSAs UNCONTROLLED WHEN PRINTED NOT PROTECTIVELY MARKED Page 27 of 60
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Level 3 PSA - EDF Hinkley Point

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